Recently I was talking to a friend and the topic of credit cards came up. I asked my friend (xx) if they had a credit card:

ところで、xxはクレジットカードを持ってる？

and got the following response:

そりゃあ持っているでしょうに。

I'm not too sure what the に at the end means, but searching around the internet it seems to be related to のに. However, sentences that end with のに typically indicate disappointment/regret etc and I don't believe that was the case here. I found this:

あなた、それくらい分かっているでしょうに。 You know that, don't you? この場合の、don't you? に相当するのが、「でしょうに」です。

which seems close in meaning, but it doesn't feel like it's from のに. Any elucidation on this would be helpful.